WTC Responders: Hints of Cancer Link

Action Points

Several types of cancer occurred significantly more often in people who worked at the site of the former World Trade Center (WTC) following the Sept. 11, 2001 terrorist attack.

Point out that people who lived or otherwise were near the site on a regular basis, but did not participate in the rescue or recovery efforts, did not have an increased risk any specific cancers, and that the findings were based on a small number of events and multiple comparisons.

Several types of cancer occurred significantly more often in people who worked at the site of the former World Trade Center (WTC) following the Sept. 11, 2001 terrorist attack, a registry study showed.

As compared with the general population of the state of New York, rescue and recovery workers at the WTC site had a 43% higher risk of prostate cancer, double the risk of thyroid cancer, and almost a three-fold higher risk of myeloma during follow-up to 2008, reported Jiehui Li, MBBS, of the New York City Department of Health and Mental Hygiene, and colleagues.

Proximity to the site did not increase the overall cancer risk, they wrote in the Dec. 19 issue of JAMA.

People who lived or otherwise were near the site on a regular basis, but did not participate in the rescue or recovery efforts, did not have an increased risk any specific cancers. Moreover, intensity of exposure to the WTC site did not increase cancer risk.

Given the mixed results, plus the small numbers that formed the basis of the results, investigators offered a cautious assessment of their findings. "Given the relatively short follow-up time and lack of data on medical screening and other risk factors, the increase in prostate and thyroid cancers and multiple myeloma should be interpreted with caution," they advised.

"The etiological role of WTC exposures in these three cancers is unclear. Longer follow-up of rescue/recovery works and participants not involved in rescue/recovery is needed with attention to selected cancer sites and to examine risk for cancers with typically long latency periods," the group added.

The collapse of the WTC towers after the terrorist attacks exposed hundreds of thousands of people to potentially toxic dust, debris, pulverized building materials, and emissions. The dust, smoke, and aerosols contained mixtures of particulate matter from a variety of known and suspected carcinogens.

Only one previous study had assessed cancer risk within the context of exposure to the WTC site. Involving 9,853 male New York City firefighters, the study showed a 19% excess cancer incidence for all sites combined for firefighters exposed to the WTC site versus unexposed firefighters (Lancet 2011; 378: 898-905).

Much of the excess cancer risk in the firefighter study could be attributed to a higher incidence of prostate and thyroid cancers, non-Hodgkin lymphoma, and myeloma, Li's group noted.

To add to the knowledge on the topic, they analyzed data from the WTC Health Registry, which contains health-related information about 55,778 people who enrolled in the registry during 2003 to 2004. Total participants include 21,850 rescue/recovery workers and 33.928 other individuals who were not involved in rescue/recovery activities.

Registry participants were followed until Dec. 31, 2008. Li and colleagues focused on cancer diagnoses during 2007 to 2008, which they considered most likely to be associated with exposure to the WTC site. For comparison of cancer rates, the investigators calculated site-specific incidences for the population of New York during 2007 to 2008.

The analysis yielded 1,187 cancers and 253,269 person-years of follow-up for participants in the WTC registry. Rescue/recovery works accounted for 439 cancers and other registry participants for the remaining 748 cancers.

Investigators performed two analyses of data on the registry participants: one involving cancer cases diagnosed from 2003 to 2006 and for cases diagnosed during 2007 and 2008.

The results showed a cancer incidence of 546.7 cases per 100,000 person-years in the WTC registry participants and 479.6 per 100,000 person-years for the general population of New York. The difference did not reach statistical significance.

Separate comparisons of the early and later cancers among registry participants showed no significant difference from the reference population: standardized incidence ratios (SIRs) of 0.94 for the early period and 1.14 for the later period.

The investigators looked at cancer incidence for 23 sites and found three significant differences between rescue/recovery workers and the general population of the state for the later period:

Prostate cancer: SIR 1.43 (95% CI 1.11 to 1.82)

Thyroid cancer: SIR 2.02 (95% CI 1.22 to 3.73)

Multiple myeloma: SIR 2.85 (95% CI 1.1 to 5.88)

The analyses revealed no significant SIRs for comparisons between the early period and the general population for either rescue/recovery workers or other registry participants.

The investigators also used information provided by registry participants to classify exposure to WTC environment as high, intermediate, and low. Highly exposed participants included rescue/recovery workers who were at the site when the towers collapsed and worked at the site in the days afterward.

Highly exposed individuals who were involved in rescue/recovery activities were defined has having two or more injuries on Sept. 11, 2001, resided in lower Manhattan, and did not evacuate the area.

Neither analysis (rescue/recovery workers or others) produced statistically different cancer rates compared with the state population.

The study had some limitations. WTC exposures were self-reported 2 to 3 years after the September 11 attacks and were subject to recall error. Also, the cancer cases identified through links with state cancer registries may have been underestimated, particularly among those without a Social Security number (about a quarter of the enrollees did not provide one).

Finally, the authors lacked data on other cancer risk factors, such as family cancer history and occupational exposures before or after September 11.

The study was supported by the National Institute for Occupational Safety and Health, the Centers for Disease Control and Prevention, and the New York City Department of Health and Mental Hygiene.

The authors reported no conflicts of interest.

Reviewed by Robert Jasmer, MD Associate Clinical Professor of Medicine, University of California, San Francisco